Ammonia is an important inorganic chemical used for a variety of purposes. One conventional process to produce ammonia uses the Haber-Bosch process in which nitrogen gas and hydrogen gas are catalytically reacted at high temperature to form ammonia according to the reaction: 3H2+N2→2 NH3. Electrolytic ammonia synthesis from water and nitrogen gas has been proposed using various molten salt systems, such as a LiCl—KCl—CsCl melt. Such molten salt systems also operate at high temperatures.
One possible use of ammonia is in a system to control NOx emissions in power plants and motor vehicles. When NOx and volatile organic compounds react in the presence of sunlight they form photochemical smog. This smog is a significant form of air pollution, especially in the summertime. Children, people with lung diseases, such as asthma, and people who work or exercise outside are susceptible to adverse effects of smog such as damage to lung tissue and reduction in lung function. Also, NOx forms nitric acid when dissolved in atmospheric moisture, forming a component of acid rain. As is well known, acid rain causes negative visual and physical affects to buildings and other structures. Furthermore, any unnatural level of nitric acid in the environment due to acid rain is undesirable.
Selective catalytic reduction (SCR) may be used to reduce NOx from emissions of internal combustion engines. Conventional SCR techniques involve injecting ammonia supplied from a tank of liquid ammonia or urea (a major component of which is ammonia) into the emissions stream of the internal combustion engines. However, the liquid ammonia supply has to be maintained and replenished. Planning and performing periodic maintenance to check and replenish urea supplies is costly and, hence, can be dismissed, despite the negative environmental effects of NOx emissions. It would be desirable to produce ammonia as needed and eliminate the need for liquid ammonia storage and replenishment.
U.S. Pat. No. 7,708,966 discloses one non-limiting example of a SCR system utilizing an on-board ammonia generation system. The disclosed on-board ammonia generation system contains a hydrogen generation cell which electrolytically splits water into hydrogen and oxygen and nitrogen generator. The hydrogen and nitrogen catalytically react to form ammonia. The disclosed process produces ammonia as needed in a motor vehicle emission control system using water from the automobile exhaust and nitrogen from air.
It would be an advancement in the art to provide the synthesis of ammonia on demand from atmospheric nitrogen and water, without the need to electrolytically split water to form hydrogen.